Contents can be distributed by any of multiple types of entities, such as by an advertiser who circulates advertising content. Advertisers can run advertisement campaigns in any of multiple different platforms, including the Internet, television, radio, printed media and billboards. Advertisements used in advertising campaigns can cover a range of products and services and can be directed toward specific audiences or more generally toward the greater population. For example, publishers operating websites can provide space to advertisers for presenting advertisements. Advertisements presented on a website are sometimes selected based on the content of the website.